In 3GPP (Third Generation Partnership Projects) which is a project aiming to standardize a mobile communication system, a radio access technology (RAT: Radio Access Technology) is standardized including GSM (registered trademark) (Global System for Mobile communications), UMTS (Universal Mobile Telecommunications System), and LTE (Long Term Evolution).
The RAT is operated in various forms by an operator. For example, a data communication service may be provided by an LTE network (or an LTE system) that supports the LTE, and a voice communication service may be provided by a 2G network (or a 2G system) that supports the GSM (registered trademark) or a 3G network (or a 3G system) that supports the UMTS.
At the same time, it is generally known that traffic of the data communication and traffic of the voice communications are different in the busiest time (Busy Hour). For example, the traffic tends to vary differently depending on each daily time zone. Therefore, the voice communication traffic may be less in a time zone with large data communication traffic, and vice versa.
For example, in a mobile communication system in which the data communication service is provided by an LTE network system and the voice communication service is provided by a 3G network, PS (Packet Switched) traffic and CS (Circuit Switched) traffic tend to vary differently.
Accordingly, depending on a certain time zone, there may be a case where there are large PS traffic and a high usage ratio of a frequency band allocated to the LTE network, and on the other hand, there are small CS traffic and a low usage ratio of a frequency band allocated to the 3G network.
Here, attention is paid to the difference in time-specific traffic between the PS and the CS, and in order to improve a frequency utilization efficiency, a frequency band re-allocation between a plurality of RATs (Spectrum Re-allocation) has been studied (see 3GPP technical report “TR 37.870 V0.2.0 (2014-05)” May 2014).